how to split array based on value in array?

Question

Basically i have an array of data, and i want to split in into 2 based on the minima of the array. I tried a for loop, but it splits it based on the magnitude of the values, rather than, effectively, if its to the left or right of that value. I guess im looking for something effectively like the split module in numpy, but that returns 2 independent seperate arrays rather than an array with subarrays in it.

node1=[]
node2=[]
for i in profile_coarse:
    if i<7.2e-10: 
        node1.append(i)
    else:
        node2.append(i)

obviously because 7.2e-10 is the minima, all the values go to node2 and node1 remains an empty array. The minima is somewhere in the middle of my data array, and i want everything that comes before it to be stored in node1 and everything after in node2. i vaguely know what np.where is, but i cant seem to apply it correctly here. how can i alter the condition of the if loop such that it works? Thanks so much for the help!

EDIT: using the idea of the index of an array, i got here:

 node1=[]
 node2=[]
for index in enumerate(profile_coarse):
    if i<get_lowest_minima(profile_coarse)[0]:                        
        node1.append(i)
    else:
        node2.append(i)
print("array node1", node1, "array node2", node2)

which doesnt work - it fills the node1 array, and leaves node2 empty...i cant figure out why. teh get_lowest_minima(profile_coarse)[0] bit is an interger element of a tuple, and profile_coarse is the array of my data. help!

hint: you care about the index of an element, not its value. read about slicing — Adam.Er8
– Adam.Er8, Commented Mar 4, 2020 at 15:25
very fair point - did not properly understand hat that was before! heres what im trying to do with that - but its not working. any ideas? edit: i put it in the question, since the formatting is much nicere there — Learn4life
– Learn4life, Commented Mar 13, 2020 at 17:23
@Adam.Er8 would really appreciate your help still! ive only just been able to pick up the project again today. — Learn4life
– Learn4life, Commented Mar 13, 2020 at 17:29

marcos · Accepted Answer · 2020-03-04 15:28:40Z

1

What you need is to find the index of the minimum value and then split the array based on that index.

import numpy as np


a = np.random.randint(0, 255, 10). # sample data [  9  33 155  48 196   3  96 185 112 104]

min_index = np.argmin(a)

node1 = a[:min_index]  # [  9  33 155  48 196]
node2 = a[min_index:]  # [  3  96 185 112 104]

answered Mar 4, 2020 at 15:28

marcos

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Riccardo Bucco · Accepted Answer · 2020-03-04 15:32:57Z

1

Here is a simple solution:

split_index = data.index(min(data))
data1 = data[:split_index]
data2 = data[split_index+1:]

You could also find the split_index with:

split_index = min(range(len(data)), key=data.__getitem__)

For more details check this question.

edited Mar 4, 2020 at 15:32

answered Mar 4, 2020 at 15:27

Riccardo Bucco

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